Limit timer for protection of X-ray tubes



Aprili 1s, 195o R. H. MORGAN I'AL LIMIT TIMER FOR PRTECTION 0F X-RAYTUBES Filed May 15, 1946 #$30k .kv @0.590,0

ANN.

nunlom Husel/ h. Morgan Hzu/ C'. Hodges machine thereby is deenergizedand voltage is removed from the high-tension transformer Il of the X-raymachine and the X-ray exposure thereby terminated. The value of theresistor 7 is chosen sc that the time required for the potentials todevelop on condenser 2 is equal to the exposure time Winch may betolerated by the X-ray tube for the lowest tube currents which will beused.

Simultaneously with the charging of the condenser 2 through the resistor'I there will also be a charging eiect through the resistor i and therectifier by a voltage developed by the transformer B in response to avoltage developed across its primary winding when current which owsthrough the X-ray tube iiows through the secondary Winding of thehigh-tension transformer I'I and the resistor I6. This current developsa potential across the resistor I6 which is impressed upon thetransformer 6. The greater the current iiowing through the X-ray tube,the greater will be the potential developed across resistor I B andapplied to the transformer 6. Depending on the value of this potential,charge will be placed upon the condenser 2 by the resistor 4. Theresistor 4 is adjusted so that the time at which the condenser 2 appliesa suiicient voltage to the thyratron I for it to become conductive willbe the maximum exposure time tolerated by the X-ray tube at the highestX-ray tube currents which are used. The rectifier tube 5 is placed inthis circuit so that the current iiowing through the resistor 4 isunidirectional; the current developed by the transformer 6 is analternating current and therefore the rectifier is needed to produce thedesired unidirectional effect.

summarizing, the resistor 1 is of such value the thyratron tube I willbecome conductive only after the maximum exposure time which may betolerated by the X-ray tube at the lowest X-ray tube currents employedand the resistors 4 and I6 adjusted to such values that the thyratrontube I will become conductive at the maximum exposure time tolerated bythe X-ray tube when operated at the highest X-ray tube currents that areemployed. At X-ray tube currents between these extremes the inventionwill limit the exposure time to values depending on the current owingthrough the X-ray tube and at such values as are Within those toleratedby the X-ray tube without causing damage.

Manifestly, many changes and modifications in the described automatictime mechanism will be apparent to those skilled in the art. For thisreason the description is intended to be illustrative only and the scopeof the invention is to be limited only as required by the followingclaims.

, Having thus described our invention what we claim as new and wish tosecure by Letters Patent is:

' l. An electronic timing mechanism for controlling the exposure time.of an X-ray tube comprising in combination anormally open supplycircuit, a source of potential connected with said circuit, -an X-raytube including the electrodes thereof, a transformer embodying primaryand secondary coils, the primary coil being connected with said supplycircuit, the secondarycoil with the electrodes of said tube, means forclosing said normally open supply circuitand initiating the exposureperiod of said X-ray tube and additional means in electrical relationwith the secondary coill of said transformer for disrupting fili saidsupply circuit and terminating the exposure period of said X-ray tube atthe expiration of the maximum exposure time tolerated by said tube atthe lowest and at the highest tube currents used, said additional meansincluding a control condenser, Ea pair of uni-directional chargingcircuits connected withrand arranged for simultaneously charging saidcondenser, one of said circuits being normally open and connected with asource of supply, the other of said charging circuits being connectedwith the secondary of said transformer, means coupled with said normallyopen supply circuit for closing the normally open charging circuit andsimultaneously inducing current iiow in the remaining charging circuitwhen the exposure period of said X-ray is initiated, each of saidcharging circuits including resistor means, the value of the resistormeans in yone of the charging circuits being such that the chargingeffect of such circuit with respect to said control condenser determinesthe maximum exposure time tolerated by said X-ray tube at the lowesttube currents used, the Value of the resistor means in the other of saidcharging circuits being such that the charging eiect of such circuitwith respect to said control condenser determines the maximum exposureperiod at the highest tube currents used.

2. An electronic timing mechanism for controlling the exposure time ofan X-ray tube comprising in combination a normally open supply circuit,a source of potential connected with said circuit, an X-ray tubeincluding the electrodes thereof, a transformer embodying primary andsecondary coils, the primary coil being connected with said supplycircuit, the secondary coil with the electrodes of said tube, saidsecondary coil including a resistor, means for closing said normallyopen supply circuit and initiating the exposure period of said X-raytube and additional means in electrical relation with the secondary coilof said transformer for disrupting said supply circuit and terminatingthe exposure period of said X-ray tube at the expiration of the maximumexposure time tolerated by said tube at the highest and at the lowesttube currents used, said additional means including a control condenser,a pair of uni-directional charging circuits connected with and effectivefor simultaneously charging said condenser, one of said chargingcircuits being normally open and connected with a source of potential,the remaining charging circuit being inductively coupled with theresistor in the secondary coil of said transformer, means coupled withsaid normally open supply circuit for automatically closing saidnormally open charging circuit and simultaneously applying the voltagedrop across said last-mentioned resistor to the remaining chargingcircuit, resistor means in each of said charging circuits, the value ofthe resistor means. in one of said charging circuits being such that thecharging effect of said circuit with respect to said control condenserdetermines the'maximum exposuretime tolerated by said X-ray tube at thelowest tube currents used, the value of the resistor means in theremaining circuit being such that its charging effect with respect tosaid control condenser determines the maximum exposure period at thehighest tube currents used.

3. An automatic electronic timing mechanism for controlling the exposuretime for an X-ray tube comprising in combination a normally open supplycircuit including a pair of normally closed contacts, a'source ofpotential connected with' said circuit, an X-ray tube including theelectrodes thereof. a transformer embodying primary and secondary coils,the primary coil being connected with said supply circuit, the secondarycoil with said X-ray tube, said secondary coil including a resistor,means for closing said normal- 1y open supply circuit to initiate theexposure period of said X-ray tube, a thyratron relay system coupled tothe secondary coil of said transformer and coacting with the normallyclosed contacts in the supply circuit, said thyratron relay systemoperating when said thyratron becomes conductive to open the normallyclosed contacts in said supply circuit, and control means in electricalrelation With said thyratron relay system to render the latterconductive at the expiration of the maximum exposure time tolerated bysaid tube at the lowest and at the highest tube currents used, saidcontrol means including a control condenser, a pair of charging circuitsconnected with and effective for simultaneously charging said condenserone of said charging circuits being normally open and connected with asource of potential, the other of said charging circuits beinginductively coupled with the resistor in the secondary coil of saidtransformer, means coupled with said normally open supply circuit forclosing the normally open circuit and simultaneously applying to theremaining circuit the voltage drop across the reslstor in the secondarycoil of said transformer, resistor means in each of said chargingcircuits, the resistor means in one of said charging circuits being suchthat the time at which said control condenser applies a suflicientvoltage to the thyratron for it to become conductive determines themaximum exposure time tolerated by the X-ray tube at the largest X-raytube currents used, the value of the resistor means connected with theremaining charging circuit being such that the time at which the controlcondenser applies a suiicient voltage to the thyratron for it to becomeconductive determines the maximum exposure time tolerated by the X-raytube at the lowest X-ray currents used.

RUSSELL H. MORGAN.

PAUL C. HODGES.

REFERENCE S CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,016,147 La Pierre et .al Oct.1, 1935 2,167,529 Scaife July 25, 1939 .2,252,530 Sweeny et al Aug. 12,1941 2,353,980 Weisglass July 18, 1944 2,384,647 Schwarzschild Sept. 111945

